Dollar-cost averaging calculator
Invest the same amount every period, get the average cost, the gain and the lump sum comparison.
In time order, separated by commas, spaces or new lines. The first number is the first purchase.
Prices and amounts are examples, not forecasts. Fractional shares, no fees or taxes. Dollar-cost averaging does not guarantee a profit or protect against a loss.
What is dollar-cost averaging?
Investing the same amount of money at regular intervals, whatever the market is doing. The SEC's Investor.gov glossary describes it as investing in equal portions at regular intervals, a pattern that can help manage risk over a long period: because the amount is fixed, you buy more shares when the price is low and fewer when it is high. It is a way to spread out when you buy, not a way to make a profit. Dollar-cost averaging does not guarantee a profit and does not protect against a loss — if the price keeps falling, every purchase loses value, and the calculator shows it when you enter a falling list of prices.
How is the average cost per share calculated?
Total invested ÷ total shares. A purchase of a fixed amount buys amount ÷ price shares, so you add up the shares from every purchase and divide everything you spent by them. Invest $100 at a price of $10 and another $100 at $20: you buy 10 and 5 shares, 15 in all for $200, which is $13.33 a share. That is lower than the simple average of the two prices, $15.00, because the same money buys more shares at the low price. The exact value of the average is the harmonic mean of the prices, n ÷ (1/p₁ + 1/p₂ + … + 1/pₙ) = 2 ÷ (1/10 + 1/20) = $13.33. The calculator shows both and they match (the harmonic mean is never above the simple average).
Is it better than investing everything at once?
It depends on the price path, which nobody knows in advance. The calculator compares the two on the prices you enter, with the whole sum invested at the first price. With the example list of 12 prices (20, 18, 15, 12, 14, 17, 19, 16, 13, 15, 18, 21) and $100 each time, the average cost is $16.05, the 74.770 shares are worth $1,570.18 at $21.00 ($370.18 gain), and the lump sum — $1,200 at $20 for 60 shares — is worth $1,260.00. When the price rises steadily the order flips: at 1% more each period, 12 purchases of $100 end at $1,268.25 against $1,338.80 for the lump sum. The comparison ignores interest on the cash that waits, fees and taxes, and it uses a price path you chose, so it shows how the method works, not what will happen.
How is this different from the stock average calculator?
The stock average calculator takes purchases you have already made, each with its own number of shares and price, and gives the average cost. This calculator plans or tests a fixed-dollar schedule: every period you spend the same amount, so the shares bought follow from the price. You enter the prices as a list, or a starting price and a steady percentage change, and it also compares the result with buying everything at the first price.
What does the calculator assume?
Fractional shares can be bought, there are no commissions, spreads, taxes or dividends, and each purchase happens at the price listed for that period. The value is taken at the last price in the list unless you enter another price. Money that has not been invested yet earns nothing in the comparison. Real brokers may sell only whole shares or add fees, which changes the figures a little.
For education only — not investment advice. Investing involves risk, including loss of principal, and dollar-cost averaging does not remove it. Sources, checked October 7, 2026: SEC Investor.gov glossary, “Dollar Cost Averaging”; Wolfram MathWorld, “Harmonic Mean” (the identity average cost = harmonic mean is checked by this site's own tests). To average purchases you have already made, use the stock average calculator; see also the compound interest calculator, ROI calculator and dividend calculator. How we check our calculators.